ukrainian defense officials say a dozen trucks have crossed into the crimean city of kurch. president obama said the united states is examining a series of steps to to, quote, isolate russia. sanctions are being prepared even right now. we have the kind of coverage that only cnn can deliver, beginning with our chief national security correspondent jim sciutto. jim? >> clearly the administration is getting ready to act. no decision made yet on whether to impose those sanctions or, indeed, which sanctions to impose but they want to have the options ready. and today we heard the president warn that his goal is to isolate russia and make its actions in ukraine very costly. with russian troops now swarming, sovereigning ukrainian territory, preparing likely sanctions against russia. president obama vowing today to make russia's military intervention a costly proposition. >> what we're indicating to the russians is that if, in fact, they continue on the projectory that they are on, we are going to have a negative impact on russia's economy and its status in the world. >> reporter: